1. Field of the Invention
The present invention relates to an image pickup apparatus and a lens unit interchangeably attachable to the image pickup apparatus such as an interchangeable lens.
2. Description of the Related Art
Such a lens unit receives, in a state of being attached to an image pickup apparatus (hereinafter referred to as “a camera”), power supplied from the camera and performs communication of commands, data and others with the camera. However, lens units of different types often operate with different operation voltages.
Japanese Patent Laid-Open Nos. 07-043773 and 2009-93122 disclose cameras to which multiple types of interchangeable lenses that operate with different operation voltages are attachable. Specifically, the camera disclosed in Japanese Patent Laid-Open No. 07-043773 is provided with multiple power sources capable of supplying source voltages respectively corresponding to the operation voltages of the multiple types of interchangeable lenses. On the other hand, the camera disclosed in Japanese Patent Laid-Open No. 2009-93122 is provided with a circuit capable of producing source voltages (that is, capable of changing a producing voltage) respectively corresponding to the operation voltages of the multiple types of interchangeable lenses.
However, the camera disclosed in Japanese Patent Laid-Open No. 07-043773 has a problem that its size becomes large because of being provided with the multiple power sources having large capacities for supplying the source voltages to the multiple types of interchangeable lenses.
Moreover, the camera disclosed in Japanese Patent Laid-Open No. 07-043773 determines the type of the interchangeable lens attached thereto on a basis of whether or not the interchangeable lens operates by a lower one of the multiple (two) source voltages (V1 and V2 lower than V1). However, the determination requires that the interchangeable lens originally operating with the source voltage V2 cannot operate with the lower source voltage V1. In other words, there is a restricted relationship between the source voltages V1 and V2. If the camera erroneously determines that the attached interchangeable lens originally operating with the source voltage V1 is one operating with the source voltage V2, the attached interchangeable lens receives, from the camera, the source voltage V2 exceeding its rated source voltage or a source current exceeding its rated source current, which causes performance deterioration or failure of the attached interchangeable lens.
On the other hand, the camera disclosed in Japanese Patent Laid-Open No. 2009-93122 determines the type of the attached interchangeable lens on a basis of a reference voltage output from the interchangeable lens to the camera. Therefore, there is no restricted relationship between the source voltages of the interchangeable lenses such as the restricted relationship between the source voltages V1 and V2 in the camera disclosed in Japanese Patent Laid-Open No. 07-043773. However, the camera disclosed in Japanese Patent Laid-Open No. 2009-93122 requires the circuit for changing the source voltage to be supplied to the attached interchangeable lens, which also increases the size of the camera. In addition, the camera is also likely to erroneously determine the type of the attached interchangeable lens, and thereby supplies, to the attached interchangeable lens, the source voltage exceeding its rated source voltage.